Ion channels play a fundamental role in the homeostasis of cell function through the regulation of the transmembrane movement of ions. Cellular activity can be affected by modifications of the activities of the ion channels. This leads to changes in membrane potential difference. Potassium channels are a diverse and ubiquitous group of ion channels. They principally regulate the resting membrane potential of the cell and attenuate the level of excitation of cells. A functional KATP channel is a hetero-octamer assembled from four inward rectifying potassium channel subunits (Kir6.2) and four sulfonylurea receptor (SUR) subunits. There are two SUR genes, SUR1 and SUR2. SUR1/Kir6.2 channels are found in the pancreas and brain. Two major splice variants arise from the SUR2 gene, SUR2A and SUR2B, that differ only at the C-terminal 42 amino acids. SUR2A/Kir6.2 channels are found in cardiac and skeletal tissues whereas SUR2B/Kir6.2 channels are found in smooth muscles of many tissues including bladder (Aguilar-Bryan, 1998). A number of diseases or conditions may be treated with potassium channel openers. This includes overactive bladder, urinary incontinence, male erectile dysfunction, female sexual disorders, premature labor, benign prostate hyperplasia (BPH), dysmenorrhea, neurodegeneration, stroke, pain, coronary artery disease, angina, ischemia, eating disorders, irritable bowl syndrome and alopecia.
Urinary incontinence (UI) is a disease that can affect the overall quality of life of a patient. Overactive bladder (OAB) is the most prevalent form of UI, with reported prevalence rate from 40 to 70% of all diagnosed UI cases (Wein, 2000). OAB is characterized by the symptoms of increased urinary frequency, urgency, and involuntary loss of urine. A primary cause of OAB is an oversensitive bladder that contracts unexpectedly and involuntarily. The ideal pharmaceutical agent should suppress the involuntary contraction while leaving the normal voiding contractions intact. ATP-sensitive potassium channel openers (KCO) could serve as such agents. The ATP-sensitive potassium channels (KATP) are expressed in bladder smooth muscle and function as key regulators of the resting membrane potential in these cells. Compounds that selectively open these channels hyperpolarize the cell and decrease cellular excitability, resulting in suppression of involuntary bladder contractions, while leaving the normal micturition circuitry intact.